The present invention relates to an object tracking method and an object tracking apparatus, and more particularly, to an object tracking method and an object tracking apparatus for controlling an imaging field (visual field range) of an imaging device in accordance with motions of an object.
While remote monitoring systems relying on an imaging device such as a TV (television) camera have been conventionally used in wide applications, many of them are so-called manned monitoring systems which employ a watchman who is monitoring while viewing images displayed on a monitor. In this type of manned monitoring system, a watchman is required to watch images displayed on a monitor at all times to identify in real time an intruding object such as a human, a car or the like which can come into a field under monitoring, so that a large burden is imposed on the watchman. Since a human has limitations in concentration, the manned monitoring system experiences overlooked intruding objects, which cannot be ignored, and therefore has a problem on the reliability. Also, as monitoring cameras become increasingly widespread, a single watchman often monitors images from a number of TV cameras on a plurality of monitors. The watchman can also overlook an intruding object when a plurality of TV cameras simultaneously capture intruding objects. Therefore, in recent years, an automatic tracking monitoring system has been highly demanded for automatically detecting an intruding object through image processing of images captured by TV cameras, instead of the human-based monitoring, automatically adjusting the visual field, viewing direction, and viewing angle of the TV cameras in accordance with motions of the intruding object, and generating a predetermined report and/or alarm.
For realizing such a system, a function is required for detecting an intruding object from an image signal, and detecting motions of the intruding object in accordance with a predetermined monitoring scheme. An example of such a monitoring scheme for detecting an intruding object is a method called a “subtraction method” (see, for example, U.S. Pat. No. 6,088,468) which has been conventionally used in wide applications. The subtraction method involves comparing an input image captured by a TV camera with a previously created reference background image, i.e., an image without intruding object to calculate, for example, a difference in luminance at each pixel, and detecting a region having a large difference value as an object.
An example of monitoring scheme for detecting a moving amount of an intruding object is a method called a “template matching method” (see, for example, “Introduction of Computer Image Processing,” pp149-153, 1985, published by Soken Shuppan Ltd.) which has been conventionally used in wide applications just like the subtraction method. The template matching method involves registering an image of an intruding object detected by a subtraction method or the like as a template, and detecting the position most similar to the template image in sequentially inputted images. Generally, when an object of interest is tracked using the template matching, the template is sequentially updated with an image of the object of interest at a position detected by the matching processing in order to follow a change in posture of the object of interest.
There is also a camera control system which sets a region which should not be captured by a monitor camera, and controls the direction of the monitor camera to avoid capturing the region which should not be captured by the monitor camera (see, for example, JP-A-9-93573).
Further, JP-A-2001-69494 discloses a monitor camera apparatus which comprises a monitor camera capable of panning over 360 degrees and tilting beyond 90 degrees, and a control function therefor, where the monitor camera holds data for masking a private zone included in an image, and masks part of the image in accordance with the data. This prior art monitor camera apparatus, however, does not have a function of tracking an intruding object.